

/**
 * @defgroup tftp TFTP server
 * @ingroup apps
 *
 * This is simple TFTP server for the lwIP raw API.
 */

#include "lwip/apps/tftp_server.h"

#if LWIP_UDP

#include "lwip/udp.h"
#include "lwip/timeouts.h"
#include "lwip/debug.h"

#define TFTP_MAX_PAYLOAD_SIZE 512
#define TFTP_HEADER_LENGTH    4

#define TFTP_RRQ   1
#define TFTP_WRQ   2
#define TFTP_DATA  3
#define TFTP_ACK   4
#define TFTP_ERROR 5

enum tftp_error {
    TFTP_ERROR_FILE_NOT_FOUND    = 1,
    TFTP_ERROR_ACCESS_VIOLATION  = 2,
    TFTP_ERROR_DISK_FULL         = 3,
    TFTP_ERROR_ILLEGAL_OPERATION = 4,
    TFTP_ERROR_UNKNOWN_TRFR_ID   = 5,
    TFTP_ERROR_FILE_EXISTS       = 6,
    TFTP_ERROR_NO_SUCH_USER      = 7
};

#include <string.h>

struct tftp_state {
    const struct tftp_context* ctx;
    void* handle;
    struct pbuf* last_data;
    struct udp_pcb* upcb;
    ip_addr_t addr;
    u16_t port;
    int timer;
    int last_pkt;
    u16_t blknum;
    u8_t retries;
    u8_t mode_write;
};

static struct tftp_state tftp_state;

static void tftp_tmr(void* arg);

static void
close_handle(void)
{
    tftp_state.port = 0;
    ip_addr_set_any(0, &tftp_state.addr);

    if (tftp_state.last_data != NULL) {
        pbuf_free(tftp_state.last_data);
        tftp_state.last_data = NULL;
    }

    sys_untimeout(tftp_tmr, NULL);

    if (tftp_state.handle) {
        tftp_state.ctx->close(tftp_state.handle);
        tftp_state.handle = NULL;
        LWIP_DEBUGF(TFTP_DEBUG | LWIP_DBG_STATE, ("tftp: closing\n"));
    }
}

static void
send_error(const ip_addr_t* addr, u16_t port, enum tftp_error code, const char* str)
{
    int str_length = strlen(str);
    struct pbuf* p;
    u16_t* payload;

    p = pbuf_alloc(PBUF_TRANSPORT, (u16_t)(TFTP_HEADER_LENGTH + str_length + 1), PBUF_RAM);
    if (p == NULL) {
        return;
    }

    payload = (u16_t*) p->payload;
    payload[0] = PP_HTONS(TFTP_ERROR);
    payload[1] = lwip_htons(code);
    MEMCPY(&payload[2], str, str_length + 1);

    udp_sendto(tftp_state.upcb, p, addr, port);
    pbuf_free(p);
}

static void
send_ack(u16_t blknum)
{
    struct pbuf* p;
    u16_t* payload;

    p = pbuf_alloc(PBUF_TRANSPORT, TFTP_HEADER_LENGTH, PBUF_RAM);
    if (p == NULL) {
        return;
    }
    payload = (u16_t*) p->payload;

    payload[0] = PP_HTONS(TFTP_ACK);
    payload[1] = lwip_htons(blknum);
    udp_sendto(tftp_state.upcb, p, &tftp_state.addr, tftp_state.port);
    pbuf_free(p);
}

static void
resend_data(void)
{
    struct pbuf* p = pbuf_alloc(PBUF_TRANSPORT, tftp_state.last_data->len, PBUF_RAM);
    if (p == NULL) {
        return;
    }

    if (pbuf_copy(p, tftp_state.last_data) != ERR_OK) {
        pbuf_free(p);
        return;
    }

    udp_sendto(tftp_state.upcb, p, &tftp_state.addr, tftp_state.port);
    pbuf_free(p);
}

static void
send_data(void)
{
    u16_t* payload;
    int ret;

    if (tftp_state.last_data != NULL) {
        pbuf_free(tftp_state.last_data);
    }

    tftp_state.last_data = pbuf_alloc(PBUF_TRANSPORT, TFTP_HEADER_LENGTH + TFTP_MAX_PAYLOAD_SIZE, PBUF_RAM);
    if (tftp_state.last_data == NULL) {
        return;
    }

    payload = (u16_t*) tftp_state.last_data->payload;
    payload[0] = PP_HTONS(TFTP_DATA);
    payload[1] = lwip_htons(tftp_state.blknum);

    ret = tftp_state.ctx->read(tftp_state.handle, &payload[2], TFTP_MAX_PAYLOAD_SIZE);
    if (ret < 0) {
        send_error(&tftp_state.addr, tftp_state.port, TFTP_ERROR_ACCESS_VIOLATION, "Error occured while reading the file.");
        close_handle();
        return;
    }

    pbuf_realloc(tftp_state.last_data, (u16_t)(TFTP_HEADER_LENGTH + ret));
    resend_data();
}

static void
recv(void* arg, struct udp_pcb* upcb, struct pbuf* p, const ip_addr_t* addr, u16_t port)
{
    u16_t* sbuf = (u16_t*) p->payload;
    int opcode;

    LWIP_UNUSED_ARG(arg);
    LWIP_UNUSED_ARG(upcb);

    if (((tftp_state.port != 0) && (port != tftp_state.port)) ||
            (!ip_addr_isany_val(tftp_state.addr) && !ip_addr_cmp(&tftp_state.addr, addr))) {
        send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Only one connection at a time is supported");
        pbuf_free(p);
        return;
    }

    opcode = sbuf[0];

    tftp_state.last_pkt = tftp_state.timer;
    tftp_state.retries = 0;

    switch (opcode) {
        case PP_HTONS(TFTP_RRQ): /* fall through */
        case PP_HTONS(TFTP_WRQ): {
                const char tftp_null = 0;
                char filename[TFTP_MAX_FILENAME_LEN + 1];
                char mode[TFTP_MAX_MODE_LEN + 1];
                u16_t filename_end_offset;
                u16_t mode_end_offset;

                if (tftp_state.handle != NULL) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Only one connection at a time is supported");
                    break;
                }

                sys_timeout(TFTP_TIMER_MSECS, tftp_tmr, NULL);

                /* find \0 in pbuf -> end of filename string */
                filename_end_offset = pbuf_memfind(p, &tftp_null, sizeof(tftp_null), 2);
                if ((u16_t)(filename_end_offset - 1) > sizeof(filename)) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Filename too long/not NULL terminated");
                    break;
                }
                pbuf_copy_partial(p, filename, filename_end_offset - 1, 2);

                /* find \0 in pbuf -> end of mode string */
                mode_end_offset = pbuf_memfind(p, &tftp_null, sizeof(tftp_null), filename_end_offset + 1);
                if ((u16_t)(mode_end_offset - filename_end_offset) > sizeof(mode)) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Mode too long/not NULL terminated");
                    break;
                }
                pbuf_copy_partial(p, mode, mode_end_offset - filename_end_offset, filename_end_offset + 1);

                tftp_state.handle = tftp_state.ctx->open(filename, mode, opcode == PP_HTONS(TFTP_WRQ));
                tftp_state.blknum = 1;

                if (!tftp_state.handle) {
                    send_error(addr, port, TFTP_ERROR_FILE_NOT_FOUND, "Unable to open requested file.");
                    break;
                }

                LWIP_DEBUGF(TFTP_DEBUG | LWIP_DBG_STATE, ("tftp: %s request from ", (opcode == PP_HTONS(TFTP_WRQ)) ? "write" : "read"));
                ip_addr_debug_print(TFTP_DEBUG | LWIP_DBG_STATE, addr);
                LWIP_DEBUGF(TFTP_DEBUG | LWIP_DBG_STATE, (" for '%s' mode '%s'\n", filename, mode));

                ip_addr_copy(tftp_state.addr, *addr);
                tftp_state.port = port;

                if (opcode == PP_HTONS(TFTP_WRQ)) {
                    tftp_state.mode_write = 1;
                    send_ack(0);
                }
                else {
                    tftp_state.mode_write = 0;
                    send_data();
                }

                break;
            }

        case PP_HTONS(TFTP_DATA): {
                int ret;
                u16_t blknum;

                if (tftp_state.handle == NULL) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "No connection");
                    break;
                }

                if (tftp_state.mode_write != 1) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Not a write connection");
                    break;
                }

                blknum = lwip_ntohs(sbuf[1]);
                if (blknum == tftp_state.blknum) {
                    pbuf_remove_header(p, TFTP_HEADER_LENGTH);

                    ret = tftp_state.ctx->write(tftp_state.handle, p);
                    if (ret < 0) {
                        send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "error writing file");
                        close_handle();
                    }
                    else {
                        send_ack(blknum);
                    }

                    if (p->tot_len < TFTP_MAX_PAYLOAD_SIZE) {
                        close_handle();
                    }
                    else {
                        tftp_state.blknum++;
                    }
                }
                else if ((u16_t)(blknum + 1) == tftp_state.blknum) {
                    /* retransmit of previous block, ack again (casting to u16_t to care for overflow) */
                    send_ack(blknum);
                }
                else {
                    send_error(addr, port, TFTP_ERROR_UNKNOWN_TRFR_ID, "Wrong block number");
                }
                break;
            }

        case PP_HTONS(TFTP_ACK): {
                u16_t blknum;
                int lastpkt;

                if (tftp_state.handle == NULL) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "No connection");
                    break;
                }

                if (tftp_state.mode_write != 0) {
                    send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "Not a read connection");
                    break;
                }

                blknum = lwip_ntohs(sbuf[1]);
                if (blknum != tftp_state.blknum) {
                    send_error(addr, port, TFTP_ERROR_UNKNOWN_TRFR_ID, "Wrong block number");
                    break;
                }

                lastpkt = 0;

                if (tftp_state.last_data != NULL) {
                    lastpkt = tftp_state.last_data->tot_len != (TFTP_MAX_PAYLOAD_SIZE + TFTP_HEADER_LENGTH);
                }

                if (!lastpkt) {
                    tftp_state.blknum++;
                    send_data();
                }
                else {
                    close_handle();
                }

                break;
            }

        default:
            send_error(addr, port, TFTP_ERROR_ILLEGAL_OPERATION, "Unknown operation");
            break;
    }

    pbuf_free(p);
}

static void
tftp_tmr(void* arg)
{
    LWIP_UNUSED_ARG(arg);

    tftp_state.timer++;

    if (tftp_state.handle == NULL) {
        return;
    }

    sys_timeout(TFTP_TIMER_MSECS, tftp_tmr, NULL);

    if ((tftp_state.timer - tftp_state.last_pkt) > (TFTP_TIMEOUT_MSECS / TFTP_TIMER_MSECS)) {
        if ((tftp_state.last_data != NULL) && (tftp_state.retries < TFTP_MAX_RETRIES)) {
            LWIP_DEBUGF(TFTP_DEBUG | LWIP_DBG_STATE, ("tftp: timeout, retrying\n"));
            resend_data();
            tftp_state.retries++;
        }
        else {
            LWIP_DEBUGF(TFTP_DEBUG | LWIP_DBG_STATE, ("tftp: timeout\n"));
            close_handle();
        }
    }
}

/** @ingroup tftp
 * Initialize TFTP server.
 * @param ctx TFTP callback struct
 */
err_t
tftp_init(const struct tftp_context* ctx)
{
    err_t ret;

    /* LWIP_ASSERT_CORE_LOCKED(); is checked by udp_new() */
    struct udp_pcb* pcb = udp_new_ip_type(IPADDR_TYPE_ANY);
    if (pcb == NULL) {
        return ERR_MEM;
    }

    ret = udp_bind(pcb, IP_ANY_TYPE, TFTP_PORT);
    if (ret != ERR_OK) {
        udp_remove(pcb);
        return ret;
    }

    tftp_state.handle    = NULL;
    tftp_state.port      = 0;
    tftp_state.ctx       = ctx;
    tftp_state.timer     = 0;
    tftp_state.last_data = NULL;
    tftp_state.upcb      = pcb;

    udp_recv(pcb, recv, NULL);

    return ERR_OK;
}

/** @ingroup tftp
 * Deinitialize ("turn off") TFTP server.
 */
void tftp_cleanup(void)
{
    LWIP_ASSERT("Cleanup called on non-initialized TFTP", tftp_state.upcb != NULL);
    udp_remove(tftp_state.upcb);
    close_handle();
    memset(&tftp_state, 0, sizeof(tftp_state));
}

#endif /* LWIP_UDP */
